At present, Li-ion batteries have mostly LiMO2 (M=Co, Ni, Mn, or combination of these transition metals) cathodes and graphite based anodes. The use of such oxide materials as cathode materials is a setback because of aspects like high cost, low stored energy density and stability. In recent years, LiFePO4 was introduced as a cathode material. This material provided a major improvement and was regarded as the solution for the large scale applications of Li-ion batteries. LiFePO4 operates at 3.5 V with the theoretical capacity of 170 Ah/kg. The PO43− units comprised therein are fixing oxygen in the structure thereby stabilizing the structure. Lacking stability is a problem for LiMO2 cathodes acting as strong oxidizing agents for organic electrolytes. LiFePO4 became a very interesting and popular material, as approx. 1000 papers were published about LiFePO4 in the last five years, and a number of companies started to produce and commercialize LiFePO4 and its composites. However, there is still a large energy density demand required for several applications, like for electric vehicles, and current cathode materials are away from satisfying this demand. Materials with higher specific energy and capacity need to be developed to enable e.g. the large scale use of plug-in electric vehicles.
V2O5 based compounds could be good alternatives for the current cathode materials, and there has been extensive research on V2O5 as a cathode material synthesized by various methods resulting in different morphologies and properties [1-3]. V2O5 theoretically should deliver a capacity of approx. 440 Ah/kg [2] for exchange of three lithium. However, the bulk material is limited by low ionic and electronic conductivity [4], and the major problem for both bulk and nano-V2O5 is irreversible capacity loss upon cycling.
As V2O5 partially transforms into ω-phase (Li3V2O5) upon cycling (LixV2O5 phases are depending on the amount of lithium inserted, α-phase (x<0.01), ε-phase (0.35<x<0.7), δ-phase (x=1), γ-phase (1<x<3) and ω-phase (x=3)) [1,2], an irreversible capacity loss occurs already in the first discharge and the theoretical capacity cannot be reached in subsequent cycles, i.e. once the ω-phase is formed this phase remains even upon withdrawal of the lithium. These problems could be reduced with amorphous-glass V2O5 systems, as some researchers already tried with V2O5—P2O5 glass as a cathode material [5]. Also for boron trioxide (B2O3) based binary, ternary, quaternary V2O5 glass systems, there had been research on vibrational, mechanical, thermal and electrical properties [6-9]. However, the own experiments with boron trioxide revealed that no glass could be obtained at up to 30 wt-% B2O3. Therefore it was the aim of the present invention to provide a boron based glass comprising a low amount of glass forming material or a high amount of cationic active material, respectively.